A Houston woman’s attempt to save drivers from a speeding ticket landed her something worse: 12 hours in jail.

As she rode her bicycle home from a grocery store last week near downtown Houston, Natalie Plummer noticed police officers pulling over speeders. After she parked her bike and turned one of her grocery bags into a makeshift sign warning drivers about the “speed trap” ahead, an officer drove up and arrested her.

But Houston police saw it differently, and arrested Plummer for standing in the street where there a sidewalk was present, a misdemeanor charge.

Houston police spokeswoman Jodi Silva said that officers found Plummer standing in the street, waving her arms as she held the sign.

But Plummer denied ever leaving the sidewalk on West Dallas Street, alleging that the arresting officer invented a reason to detain her.

“He couldn’t take me to jail for holding up this sign or he would have. So all he could do was make up something fake about it,” Plummer told KRTK. The officer searched Plummer’s backpack, she said, and threatened to arrest her for obstructing justice, a felony charge.

After being held in jail for 12 hours, Plummer was released on bond, and will soon appear in court to face her misdemeanor charge.

While Plummer’s method of alerting drivers to police activity might have been unprecedented, state laws covering such warnings are decades old. Their most common form, flashing headlights, is legal in some states but illegal in others.

Laws in New Jersey, New York, Ohio, Pennsylvania, Tennessee, Virginia and Florida allow headlight flashing, while other states, such as Arizona and Alaska, forbid it. In Washington, drivers may be fined $124 for flashing their high beams within 400 feet of another vehicle for any reason. Other states forbid headlight flashing in some circumstances but not in others.